View full sizeU.S. Geological SurveyBefore and after photos of damage by Isaac's surge and waves to the northern end of the Chandeleur Islands. The yellow arrow points to the same feature in each image. The view looks west from the Gulf of Mexico across the BP oil protection berm to a remnant of the island in the before picture. The berm appears to have disappeared during the storm.

"It gave me pause," said USGS oceanographer Asbury Sallenger, who is leading a team of scientists mapping Isaac's damage to the Chandeleurs in Louisiana and Dauphin Island in Alabama. "There's no question there are significant changes out there."

The crescent-shaped barrier island chain, a remnant of an ancient delta of the Mississippi River, has been repeatedly sliced into pieces during the past three decades by hurricanes. Some of the sand washed away by past storms' surge and waves has slowly returned to the island chain during several years following each storm, but the remaining footprint of the islands has been steadily shrinking.

In the immediate aftermath of the BP spill, state officials saw building a berm as a way to both capture oil and extend the life of the islands. But the project simply moved sand from offshore onto a line extending north from the eroded edge of the northernmost island, without additional features aimed at keeping the sand in place during hurricanes.

State officials got BP to set aside $360 million to build the berms to capture oil before it entered Louisiana's fragile wetlands, but the Army Corps of Engineers agreed to permit only about 39 miles of the more than 120 miles of berms requested by the state.

View full sizeU.S. Geological SurveyMap shows location of photos available on the U.S. Geological Survey's Hurricane Isaac web site.

Only about 10 percent of the first berm along the northern part of the Chandeleurs was completed by July 15, 2010, when BP capped the Macondo well, and the National Oil Spill Commission later concluded that the berms captured, at most, only 1,000 barrels of oil.

The Chandeleur berms were completed in March 2011, and state officials then convinced BP to allow use of about $100 million not yet spent to turn several of the berms west of the Mississippi River into comprehensive barrier island restoration projects.

Coastal Planning & Engineering Inc. vice president Gordon Thomson told the state Coastal Protection and Restoration Authority in April that the Chandeleur berms had actually grown, the result of sand drifting onto the islands from the area where it was dredged for the project, or elsewhere.

But because the Chandeleurs are protected as part of the Breton National Wildlife refuge, the nation's second national refuge, the state and the U.S. Fish & Wildlife Service did not use any of the BP money for a more comprehensive barrier island restoration project for the islands.

Isaac's four-hour stall just west of the river late Tuesday and early Wednesday and its slow forward speed before and afterward, turned it into a sand clearing machine, with its effect seen as far away as Dauphin Island, just east of Mobile Bay, Sallenger said.

"The way the storm slowed down right when it got to you guys really added to the problem," Sallenger said. "We compare it to a nor'easter on the East Coast that blows for 24 hours or longer, rather than a hurricane that buzzes through."

Isaac's most significant damage was to the northern end of the Chandeleurs, Sallenger said. Several locations in the central and southern parts of the chain fared better, possibly because they were made of more consolidated material than the new berms.

Sallenger said the Geological Survey is using aerial LIDAR, a laser form of radar, to develop a more detailed map of the islands, a process that will take another two weeks. Until then, remaining high water in the area from Isaac may be masking some parts of the remaining northern islands, he said.

At Dauphin Island, the surge took advantage of weak areas just east and west of a wall that was built to plug a wide cut created in 2005 by Hurricane Katrina, Sallenger said.

View full sizeU.S. Geological SurveyIsaac's surge and waves created a new cut in Dauphin Island just east of a wall built to close a gap created during Hurricane Katrina.

The aerial photos released Thursday also show that driveways cut through a tall sand dune rebuilt on the Gulf side of the island after Katrina acted as nozzles, funneling sand from the Gulf beach and dune inland.

Sallenger said this latest effort by the island's sand to roll north towards the mainland is a common process for Gulf barrier islands.

But Isaac's surge and waves were apparently not high enough to destroy many of the elevated homes on the less-protected western end of the populated part of the island.